In a lawsuit that pits two tech giants against each other, Alphabet is alleging that one of Uber's top executives stole proprietary designs for a self-driving system.

The executive at the center of that suit is Anthony Levandowski, who joined Uber in August 2016 as part of Uber's acquisition of his self-driving startup Otto. Prior to that, Levandowski was one of the top engineers at Alphabet's car division, now called Waymo.

To bolster its suit, Alphabet laid out a detailed timeline of Levandowski's relationship with Uber executives, including CEO Travis Kalanick. According to Alphabet, that relationship dates back to the summer of 2015, approximately six months before Levandowski even left Alphabet.

Now, sources are adding more to that claim. Kalanick hired Levandowski as a consultant to Uber's fledgling self-driving effort as early as February 2016, six months before Levandowski publicly got his company off the ground, according to three sources.

It's not entirely uncommon for engineers to consult for other companies, but the timing of Levandowski's hiring at Uber so close to the initial formation of Otto raises a number of questions.

Otto was officially formed on Feb. 1, 2016. Sources say Levandowski began appearing at Uber's Pittsburgh offices, where it develops self-driving technology, between February and March 2016.

There are obvious questions. Why would someone in the midst of starting his own self-driving company advise a potential competitor? Why would Kalanick — a pugnacious CEO known to be ultra competitive — trust someone starting their own self-driving company to guide his own?

Some in the developer community have speculated that Kalanick intended to poach Levandowski ever since his time at Alphabet, with Levandowski starting Otto as a way to create a credible, arms-length technology outside of Alphabet.

Uber declined to comment for this story.

Kalanick, who was known to perpetuate a win-at-all-cost culture at Uber, had become frustrated by the progress of the company's self-driving group, according to the sources.

Uber poached swaths of engineers from Carnegie Mellon's robotics institute in early 2015 to create its own self-driving tech. Originally, the department's directors had planned to begin testing robot cars on public roads by August 2016.

Once it became clear that the team would not meet that deadline, Kalanick brought in Levandowski, sources say. Shortly after that, Otto launched out of stealth in May.

If nothing else, Uber's acquisition of Otto six months later made one thing clear: The going rate for top engineering talent was close to $700 million. Levandowski was a lead engineer at Google's self-driving project, after all.

Still, it came as a surprise to many, as the company was reportedly self-funded and had been scooped up a mere six months after it had launched publicly.

But if the timeline laid out in Alphabet's suit against Uber is true, Levandowski's conversations with Uber executives about Otto may have begun before Otto even launched.